A polycarbonate resin is excellent in transparency, heat resistance and impact resistance, and is widely used in an optical medium field, an electric, electronic and office automation filed, an automobile and industrial machinery field, a medical field, and other various industrial fields. An aromatic polycarbonate, which is ordinarily used currently, is produced from raw materials obtained from petroleum resources. Accordingly, in view of the existing situations of concern, e.g., exhaustion of petroleum and global warming due to carbon dioxide generated on incineration of waste products, such a material is expected that has properties equivalent to an aromatic polycarbonate but involves reduced environmental load.
Under the circumstances, a dianhydrohexitol compound (such as isomannide, isoidide and isosorbide), which is an anhydrosugar alcohol, can be derived from a plant-derived raw material, such as mannitol, iditol and sorbitol, and is being studied as a regenerable resource (i.e., a resource that differs from exhaustible natural resources such as petroleum and coal but has a regeneration capability by itself, such as forest resources, biomass, wind power and small-scale hydroelectric power generation) for producing a polymer, particularly polyester and polycarbonate. In particular, a polymer produced with isosorbide, which is produced from inexpensive starch and is easily available commercially since it is used as a medical raw material, has been earnestly investigated (see, for example, Patent Documents 1 to 3).
Furthermore, a carbonate obtained by copolymerizing, as a diol component, a glycol compound or the like used as a polyester raw material, in addition to isosorbide, is being studied (see, for example, Patent Documents 4 and 5). This is because a polycarbonate containing only isosorbide as a diol component involves such problems as difficulty in molding due to the considerably high melt viscosity thereof derived from the rigid structure. A dianhydrohexitol compound is significantly expensive as a raw material for a polymer, which brings about a problem in cost. In other words, the cost for raw materials can be advantageously reduced by copolymerizing an inexpensive glycol compound in such a range that the necessary polymer properties can be maintained.
Apart from the matters, the most notable problem appearing in the conventional investigations is that a polymer produced with an anhydrosugar alcohol, such as isosorbide, is inferior in hue as compared to an ordinary polymer produced with a petroleum raw material, and thus there are difficulties on commercialization and spread of usage of the polymer thereby.
It has been known that an anhydrosugar alcohol compound is decomposed or denatured under some storage conditions, and various studies have been made for improving the stability thereof. For example, Patent Document 6 discloses that a particular reducing agent or antioxidant, such as sodium boron hydride, is added as a stability improving agent at a particular timing in the production process of an anhydrosugar alcohol, thereby improving the stability thereof on storing at 40° C.
Patent Document 1
    British Patent No. 1,079,686Patent Document 2    U.S. Pat. No. 4,506,066Patent Document 3    WO 2007/013463Patent Document 4    WO 2004/111106Patent Document 5    JP-A-2003-292603Patent Document 6    WO 2003/043959 (US-A 2003/0097028 and JP-T-2005-509667)